Latency between Azure Web App and a VM

Hi

I have an Azure Web App and an Azure VM running in the same data center under the same VNet. The web app can properly connect to the VM using its internal IP (as well as using the DNS server I've configured).
The VM runs the web app's database (SQL Server) thus I'd like the network latency to be the lowest possible (this is why I've put both machine in a VNet).
My question is how should I measure the latency ?
From within the VM, using "psping -l 1k -n 1000 -h 20 <public_url>:80" is ok when using the public address, but I wanna check the latency using the web app's internal IP and this cannot be resolved.

Thanks,
Noam.